This cluster of papers explores the evolutionary origins, ecological consequences, and molecular mechanisms of endophyte symbiosis with grasses. It investigates the adaptations of endophyte-infected grasses to environmental stresses, the role of alkaloid biosynthesis in plant stress tolerance, and the coevolutionary dynamics between host plants and mutualistic fungi. The research also delves into the impact of endophytic fungi on grassland ecosystems and their potential applications in agriculture.